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Date: Tue, 17 Nov 2015 00:14:11 +0000 (UTC)
From: "Tsz Wo Nicholas Sze (JIRA)" <jira@apache.org>
To: hdfs-dev@hadoop.apache.org
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Subject: [jira] [Created] (HDFS-9434) Recommission a datanode with 500k
 blocks may pause NN for 30 seconds
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Tsz Wo Nicholas Sze created HDFS-9434:
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             Summary: Recommission a datanode with 500k blocks may pause NN for 30 seconds
                 Key: HDFS-9434
                 URL: https://issues.apache.org/jira/browse/HDFS-9434
             Project: Hadoop HDFS
          Issue Type: Improvement
          Components: namenode
            Reporter: Tsz Wo Nicholas Sze
            Assignee: Tsz Wo Nicholas Sze


In BlockManager, processOverReplicatedBlocksOnReCommission is called within the namespace lock.  There is a (not very useful) log message printed in processOverReplicatedBlock.  When there is a large number of blocks stored in a storage, printing the log message for each block can pause NN to process any other operations.  We did see that it could pause NN  for 30 seconds for a storage with 500k blocks.

I suggest to change the log message to trace level as a quick fix.


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